即使我使用 DB_CLOSE_DELAY=-1 报告 H2 内存数据库也找不到表
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【中文标题】即使我使用 DB_CLOSE_DELAY=-1 报告 H2 内存数据库也找不到表【英文标题】:H2 in-memory database even if I use DB_CLOSE_DELAY=-1 reports Table not found 【发布时间】:2021-04-23 08:18:34 【问题描述】:我正在使用 h2 数据库作为 maven 项目的依赖项:
<dependency>
<groupId>com.h2database</groupId>
<artifactId>h2</artifactId>
<version>1.4.200</version>
</dependency>
要使用in-memory mode我已经配置了application.properties
文件:
jdbc:h2:mem:test;DB_CLOSE_DELAY=-1
如提到的here 和here,因为对于变体:jdbc:h2:mem:test
。
数据库的内容在最后一次连接的那一刻丢失 已关闭。
同时,我使用 Intelij Idea 配置了数据源:
下一步,我已经使用带有 h2-dialect 的脚本成功填充了数据:
CREATE TABLE users
(
id int NOT NULL GENERATED BY DEFAULT AS IDENTITY,
login varchar(10),
PRIMARY KEY (id),
UNIQUE (login)
);
CREATE TABLE teams
(
id int NOT NULL GENERATED BY DEFAULT AS IDENTITY,
name varchar(10),
PRIMARY KEY (id)
);
CREATE TABLE users_teams
(
user_id int,
team_id int,
FOREIGN KEY (user_id)
REFERENCES users (id) ON DELETE CASCADE,
FOREIGN KEY (team_id)
REFERENCES teams (id) ON DELETE CASCADE,
UNIQUE (
user_id,
team_id
)
);
填充后连接没有关闭,但是如果我在连接过程中运行程序,我仍然会收到错误:
jan 19, 2021 3:50:01 AM com.epam.rd.java.basic.practice8.db.DBManager insertUser
Table "USERS" not found; SQL statement:
INSERT INTO users (login) VALUES ('petrov'); [42102-200]
jan 19, 2021 3:50:01 AM com.epam.rd.java.basic.practice8.db.DBManager insertUser
Table "USERS" not found; SQL statement:
INSERT INTO users (login) VALUES ('obama'); [42102-200]
jan 19, 2021 3:50:01 AM com.epam.rd.java.basic.practice8.db.DBManager findAllUsers
Table "USERS" not found; SQL statement:
SELECT * FROM users; [42102-200]
jan 19, 2021 3:50:01 AM com.epam.rd.java.basic.practice8.db.DBManager insertTeam
Table "TEAMS" not found; SQL statement:
INSERT INTO teams (name) VALUES ('teamB'); [42102-200]
jan 19, 2021 3:50:01 AM com.epam.rd.java.basic.practice8.db.DBManager insertTeam
Table "TEAMS" not found; SQL statement:
INSERT INTO teams (name) VALUES ('teamC'); [42102-200]
jan 19, 2021 3:50:01 AM com.epam.rd.java.basic.practice8.db.DBManager findAllTeams
Table "TEAMS" not found; SQL statement:
SELECT * FROM teams; [42102-200]
jan 19, 2021 3:50:01 AM com.epam.rd.java.basic.practice8.db.DBManager getUser
Table "USERS" not found; SQL statement:
SELECT * FROM users WHERE users.login='petrov'; [42102-200]
jan 19, 2021 3:50:01 AM com.epam.rd.java.basic.practice8.db.DBManager getUser
Table "USERS" not found; SQL statement:
SELECT * FROM users WHERE users.login='ivanov'; [42102-200]
jan 19, 2021 3:50:01 AM com.epam.rd.java.basic.practice8.db.DBManager getUser
Table "USERS" not found; SQL statement:
SELECT * FROM users WHERE users.login='obama'; [42102-200]
jan 19, 2021 3:50:01 AM com.epam.rd.java.basic.practice8.db.DBManager returnTeam
Table "TEAMS" not found; SQL statement:
SELECT * FROM teams WHERE teams.name='teamA'; [42102-200]
jan 19, 2021 3:50:01 AM com.epam.rd.java.basic.practice8.db.DBManager returnTeam
Table "TEAMS" not found; SQL statement:
SELECT * FROM teams WHERE teams.name='teamB'; [42102-200]
jan 19, 2021 3:50:01 AM com.epam.rd.java.basic.practice8.db.DBManager returnTeam
Table "TEAMS" not found; SQL statement:
SELECT * FROM teams WHERE teams.name='teamC'; [42102-200]
jan 19, 2021 3:50:01 AM com.epam.rd.java.basic.practice8.db.DBManager findAllUsers
Table "USERS" not found; SQL statement:
SELECT * FROM users; [42102-200]
Exception in thread "main" java.lang.NullPointerException
===========================
===========================
===========================
at com.epam.rd.java.basic.practice8.Demo.main(Demo.java:382)
我也试过用:
jdbc:h2:mem:test;IFEXISTS=FALSE
如here 所述,但在连接过程中出现同样的问题。
演示类的逻辑如下:
public class Demo
private static <T> void printList(List<T> list)
for (T element : list)
System.out.println(element);
public static void main(String[] args)
DBManager dbManager = DBManager.getInstance();
dbManager.insertUser(User.createUser("petrov"));
dbManager.insertUser(User.createUser("obama"));
printList(dbManager.findAllUsers());
System.out.println("===========================");
dbManager.insertTeam(Team.createTeam("teamB"));
dbManager.insertTeam(Team.createTeam("teamC"));
printList(dbManager.findAllTeams());
System.out.println("===========================");
User userPetrov = dbManager.getUser("petrov");
User userIvanov = dbManager.getUser("ivanov");
User userObama = dbManager.getUser("obama");
Team teamA = dbManager.getTeam("teamA");
Team teamB = dbManager.getTeam("teamB");
Team teamC = dbManager.getTeam("teamC");
dbManager.setTeamsForUser(userIvanov, teamA);
dbManager.setTeamsForUser(userPetrov, teamA, teamB);
dbManager.setTeamsForUser(userObama, teamA, teamB, teamC);
for (User user : dbManager.findAllUsers())
printList(dbManager.getUserTeams(user));
System.out.println("~~~~~");
System.out.println("===========================");
dbManager.deleteTeam(teamA);
teamC.setName("teamX");
dbManager.updateTeam(teamC);
printList(dbManager.findAllTeams());
谁能解释一下,为什么会出现这个错误:
默认情况下,关闭与数据库的最后一个连接会关闭 数据库。对于内存数据库,这意味着内容丢失。 要保持数据库打开,请将 ;DB_CLOSE_DELAY=-1 添加到数据库 URL。 将内存数据库的内容与虚拟数据库一样长 机器还活着,使用 jdbc:h2:mem:test;DB_CLOSE_DELAY=-1。
【问题讨论】:
【参考方案1】:您从 IntelliJ 启动的 H2 的嵌入式内存实例在不同的进程中运行,并且与您的应用程序的嵌入式 H2 实例无关。您正在处理两个独立的数据库,您的应用程序看不到您使用 IntelliJ 创建的表。
如果您需要使用嵌入式内存数据库,那么您还需要从应用程序本身创建数据库架构。例如,通过executing a SQL script on connection 或使用架构演化工具,如Flyway 或Liquibase。 Spring Boot 等框架也可以配置为执行Database Initialisation
如果您确实需要多个进程来访问同一个数据库实例,那么您需要在 Server Mode 中运行 H2(如果您从应用程序以编程方式启动服务器,它适用于内存数据库)或 @987654326 @(不适用于内存数据库)。
【讨论】:
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